Process for the production of tetraethyl lead



Dec. 18, 1962 Filed June 9, 1958 K. ZIEGLER ET AL PROCESS FOR THEPRODUCTION OF TETRAETHYL LEAD 2 Sheets-Sheet l STORAGE STORAGE I/'DIAPHRAGM "SETTLING I rowan /s 1 I (a? me I STORAGE STORAGE I I 23 /8:r/7

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INVENTORS KARL Z/EGL ER. HERBERT LE HMKUHL ATTORN S atent 3,069,334Patented Dec. 18, 1962 Free 3,069,334 PROCESS FOR THE PRUDUCTION OFTETRAETHY L LEAD Karl Ziegler and Herbert Lehmkuhl, Mulheim (Ruhr),Germany; said Lehmkuhl assignor to said Karl Ziegler, Mulheim (Ruhr),Germany Filed June 9, 1958, Ser. No. 740,623 Claims priority,application Germany June 12, 1957 22 Claims. (Cl. 204-59) This inventionrelates to a process and a device for the production of tetraethyl lead.

In our co-pending patent application Serial No. 548,862, filed November25, 1955, now Patent No. 2,985,568, a process is described for theproduction of lead tetraalkyls. This process allows an overall resultcharacterized by the reaction equation:

Since a direct reaction between metallic lead, hydrogen and olefins isnot possible, the above result is realized by a combination of twoprocess steps. Aluminum is re acted in the first step with an olefin andhydrogen to form aluminum trialkyl. In the second step the aluminumtrialkyl is made electrically conductive by the addition of a suitablecompound, such as an alkali metal halide, and subsequently electrolizedbetween an anode containing lead and a cathode of any suitable material.In this step, aluminum is deposited at the cathode while lead tetraalkylis formed at the anode and is separated from the electrolyte. Thealuminum deposited at the cathode may afterwards be reacted again withan olefin and hydrogen to form aluminum alkyl which is recycled into theprocess. The reaction of the aluminum with an olefin and hydrogen in thefirst step may be effected pursuant to our co pending applicationsSerial No. 484,576, filed January 27, 1955, and Serial No. 573,470,filed March 23, 1956, and Patent No. 2,835,689, according to thefollowing reaction equation:

(2) 2AlR +Al+1 /2H =3AlHR and may, if desired, be effected in aluminumhalide catalyst.

In order to make the aluminum alkyl compounds electr1cally conductivethe above mentioned applications suggest the use of additives such as analkali halide, especially sodium fluoride. According to applicationSerial No. 548,862 a particularly suitable electrolyte consists of theliquid complex compound of the composition NaF.2AlR which is describedin application Serial No, 379,294, filed September 9, 1953, of theapplicant, now Patent No. 2,844,615.

The direct production of lead tetraalkyl as proposed in applicationSerial No. 548,862 may be represented by the following reactionequation:

During the electrolysis, aluminum trialkyl is thus constantly used tothe same extent as the lead tetraalkyl and metallic aluminum are formed.When NaEZAlR is used as the electrolyte, this has the effect ofconstantly impoverishing the electrolyte in aluminum so that theelectrolyte composition finally reaches a ratio of NaF:AlR of about 1:1,with the formation of a definite complex compound NaF.AlR (1:1compound). This compound may have a high melting point and asubstantially lower conductivity than the compound of the type NaF.2AlR(1:2 compound) and is therefore less suited for the electrolysis, e.g.for economic reasons. It is apparent that stationary conditions can bemaintained in the electrolyte if aluminum the presence of a dialkyltrialkyl is constantly added at the same rate that it is being consumed,with the formation of lead tetra-alkyl at the anode and aluminum at thecathode.

In the further development of the process it became apparent that unlessspecial precautionary measures were taken, the aluminum deposited at thecathode would react with the lead tetraalkyl forming lead whichcontaminated the rest of the aluminum. This effect increasedproportionately with an increase in the current density used for theelectrolysis. When using higher current densities the aluminum is notdeposited at the cathode in form of a compact metal but as a porouspowder which reacts with the lead tetraalkyl much more rapidly. Thesehigher current densities are, however, desirable for economic reasons.The contaminated aluminum thus obtained is not pure aluminum suitablefor industrial purposes, and if used for the conversion to aluminumalkyl compounds in the production of lead tetraalkyl, complicates theprocess.

In said application Serial No. 548,862 it was proposed to separate theelectrolytic cell by means of a diaphragm into an anode and a cathodespace, in order to prevent the contamination of the catholyte with thelead tetraethyl containing anolyte and thus to obtain a refinedaluminum. The separation of the anode from the cathode space has,however, far reaching consequences for the electrolysis. The chemicalreactions occurring during the electrolysis change the composition ofthe now separate catholyte and anolyte. The diaphragm prevents acomingling of these two liquids and thus an adjustment of thedifferences in the composition of the electrolyte resulting during theelectrolysis. Consequently during the electrolysis aluminum trialkylfree from complex bonding with alkali halide is formed in the anodespace. This free aluminum trialkyl is removed together with the leadtetraalkyl and can be separated from it only with difficulty. In thismanner, a part of the aluminum is lost during the process in the form ofaluminum trialkyl which contaminates the lead tetraalkyl obtained.

The applicants have proposed overcoming this difliculty by adding acertain amount of sodium aluminum tetraalkyl to the electrolyte at thebeginning of the electrolysis.

It was found, however, that this modification of the process was notsufiicient to avoid with certainty the above mentioned complicationsresulting from the separation of the electrolysis device into anode andcathode space.

One object of this invention is to avoid all the above mentioneddifiiculties and allow the deposition of aluminum at the cathode whichis suitable to be used as refined aluminum outside the process, and theproduction of lead tetraethyl which does not contain any aluminumtriethyl at the anode. This and still further objects will becomeapparent from the following description read in conjunction with thedrawings in which:

FIG. 1 is a diagrammatic perspective view of an embodiment of anarrangement of electrolysis cells for effecting the process inaccordance with the invention;

FIG. 2 diagrammatically shows'an arrangement in the form of a flow sheetfor effecting the process in accordance with the invention; and

FIG. 3 is a fiow sheet showing a further embodiment of the process inaccordance with the invention. a

The invention relates to an improvement in the above described processfor the electrolytic production of tetraethyl lead by passing anelectrolysis current between a cathode and lead-containing anode throughan aluminum triethyl-containing electrolyte. In accordance with theinvention a diaphragm is maintained between the cathode and anode tothereby form separate cathode and anode spaces which are separated fromfree flow communication of the electrolyte with each other by means ofthe diaphragm. At least initially in anolyte is maintained in Theelectrolysis may be continued until one of the NaAl(C H and NaF.Al(C Hhas disappeared The advantages obtained by the process according to theinvention are apparent from a consideration of the chemical reactions inthe anolyte during the electrolysis.

For the purpose of illustrating the process of the invention it will besupposed that the complex compound NaF.2Al(C H is present in the anolytemixture. As will be seen later, this is not absolutely necessary. The1:2 compound decomposes into positive sodium ions and the negativecomplex-radical These ions are discharges at the anode where, in thepresence of lead going into solution, the following reaction occurs Inthe brackets at the right side of the equation there appears thus atfirst a double molecule This decomposes into its two components Thesodium ions which, so to speak, remain behind in the anode space partlytransfer to the cathode space and partly find their electrochemicalequivalent in the fluorine ions transferring through the diaphragm intothe anode space.

For each C H group bound to lead going into solution there thus resultsone free Al(C H compound. This can only be combined as 1:1 compound tothe extent to which sodium ions did not move out of the anode space andfluorine ions did transfer into the anode space from the cathode space.

Moreover, the Al(C H F compound formed according to Equation 4 has thegreater tendency towards forming complexes than the Al(C H compound. Asa result, a reaction with the excess electrolyte according to takesplace.

For each C H group bound to the lead, a substantial amount of aluminumtriethyl is thus liberated and separated in admixture with thetetraethyl lead.

According to the process of the. invention the electrolysis is startedwith an anolyte which contains one compound each of the formula NaAl(C Hand of the formula NaF.Al(C H (1:1 compound). The effect of theseadditions is illustrated by the following reaction equation;

The combination of the Equations 4 and 5 results in the new reactionequation:

(transferring to the cathode).

The NaAl(C I-I compound, which in accordance with the invention isadditionally present, enters the reaction in the following manner:

Of the three Al(C H compounds formed according to Equation 7 only twocan react to a 1:2 compound so that one Al(C H compound is left whichcould contaminate the lead tetraethyl.

Further according to the invention, the anolyte contains additional free1:1 compound. This 1:1 compound combines with the remaining aluminumtriethyl under formation of a 1:2 compound so that the anolyte now isfree of Al(C H According to Equation 4, for each one fourth Pb(C H oneAl(C H compound is liberated and one Al(C H F compound formed whichrequires for its neutralisation exactly one NaAl(C H It is, therefore,suitable if the 1:1 compound and the NaAl(C l-I compound are added tothe anolyte mixture in equivalent amounts, although this equivalence isnot critical. The reaction results are not affected if there is no suchequivalence; only in that case the electrolysis is suitably discontinuedat the very point at which the component of which there is a deficiencyhas just disappeared or preferably even a little earlier. It ispreferred to keep the molar proportion of NaAl (C H 3 in the range of3:1 to 1:3 with the commercial optimum of one mole NaAl(C H,-,) to onemole 1:1 compound.

As is apparent from the above equations, the 1:2 compound is formedduring the electrolysis from the anolyte components, the 1:1 compoundand the NaAl(C- H compound. As a result, an anolyte mixture isconceivable which contains originally only NaF.Al(C H (1:1) compound andNaAl(C H compound and no additional 2:1 compound. In practice, however,an anolyte mixture of this type has certain disadvantages. The meltingpoint is high so that high reaction temperatures are required. Theconductivity is low since the 1:1 compound has a considerably lowerconductivity, amounting to about only one fiftieth of the conductivityof the 1:2 electrolyte.

In practice, a particularly suitable anolyte contains per mole NaAl(CI-l one mole of the 1:1 compound and 0.16 to 1.70 moles and preferably0.67 to 1.70 moles of the 1:2 compound.

If the electrolysis is continued until these electrolytes in the anodespace have exactly the composition then they contain 10 to 20%,preferably 10 to 15% lead tetraethyl partly in solution, partlyseparated in liquid form. Per kg. electrolyte a current of 33 /3 to 66%ampere hr., preferably 33 /3 to 50 ampere hr. is required.

With these electrolyte mixtures it is of course not absolutely essentialthat the amount of current is exactly as indicated. The stated amountsrepresent the limit up to which the formation of free aluminum triethylis avoided. tetraethyl continues to be formed; however, according to theabove equations and in the absence of at least one of the electrolytecomponents used in accordance with the invention, free aluminum triethylwill be formed which comingles with the lead tetraethyl.

Suitably, the composition of the anolyte and the amount of the currentto be applied will be so selected that upon If the electrolysis isfurther continued, lead removal of the used anolyte the 1:1 compound hasbeen reacted as far as possible. On the one hand an incomplete reactionprevents the substantially optimum utilisation of the electrolyte forthe production of lead tetraethyl which is desirable for economicreasons. On the other hand, the 1:1 compound is more readily solublethan the 2:1 compound in the subsequent extraction of the electrolytefor the recovery of the lead tetraethyl, thereby interfering with therecovery of the lead tetraethyl. It is best to remain a few percentbelow the amount of the required ampere/hours since this gives theguarantee that on the one hand the reaction has progressed as far aspossible whereas on the other hand the critical limit at which onecomponent part of the electrolyte disappears has not yet been exceeded.

Also for the development in the cathode space, the separation of theelectrolysis device by a diaphragm preventing the admixing of anolyteand catholyte has far reaching consequences. As a result of thearrangement of the device in accordance with the invention thecomposition of the catholyte is thus without any importance for theformation of lead tetraethyl in the anode space. Thus, any cathodeliquid may be used provided it fulfills the condition of not becomingadmixed with the anolyte through the interposed diaphragm and notsubstantially interfering with the current transport. For an economicoperation of the process under regeneration of the used up aluminumalkyl compound, it is however suitable to use also in the cathode spacean electrolyte which contains an aluminum ethyl compound.

If the original catholyte contains the complex compound NaF.2Al(C H thensodium is primarily separated during the electrolysis. This sodiumreacts with /sAl(C H to /3Al+NaC H which upon addition to Al(C H formsNaAl(C H (sodium aluminum tetraethyl). At the same time, fluorine ionspass through the diaphragm into the anode space and vice versa sodiumions from the anode space into the cathode space. In the course of theelectrolysis, more and more NaAl(C H is formed at the cathode. At thesame time the aluminum triethyl disappears and as a result the 1:1compound is developed from the 2:1 compound.

Suitably the 1:2 compound is thus used at the beginning of theelectrolysis as catholyte. As a result of the primary separation ofsodium at the cathode, the immediate reaction with /sAl(C I-I to sodiumethyl and /3A1 there disappears for each separated equivalent aluminum/aAl(C H The simultaneously obtained sodium ethyl reacts with a furtherAl(C H compound I to NaAl(C H For each Na(C H there thus disappear ,Al(CI-I in other words, 1:1 compound are being formed from the originallypresent 1:2 compound. As was just pointed out above, in the anode spaceon the other hand just one NaAl(C H and one NaF.Al(C I-I (1:1 compound)react to the 1:2 compound.

Upon suitable selection in the composition of the anode and cathodeliquids at the beginning of the electrolysis there thus exists accordingto the invention the possibility to regenerate the used up catholyte byaddition of an amount of aluminum triethyl corresponding toapproximately the amount of aluminum deposited at the cathode whichcatholyte is subsequently used as anolyte. Vice versa, there exists thepossibility to free the used up lead tetraethyl containing anolyte ofthis lead tetraethyl and to subsequently use it as catholyte.

According to the invention, the mutual exchange. of the anolyte andcatholyte may be effected intermittently by electrolysing one chargeuntil anolyte and catholyte have the optimum composition for theexchange. Now the entire catholyte is removed, an amount of freshaluminum triethyl approximately equivalent to the amount of separatedaluminum added and subsequently introduced as one charge into the anodespace from which the entire anolyte has been previously removed as onecharge. This 6 anolyte is freed of lead tetraethyl and subsequentlyintroduced into the emptied cathode space.

According to the invention the process may, however, also be carried outcontinuously by continuously withdrawing a certain proportion of bothliquids, freeing the Withdrawn anolyte from the lead tetraethyl andadding fresh aluminum trialkyl to the catholyte and subsequentlyreturning both portions into the other electrolyte space. In place ofthe intermittent exchange of the electrolyte liquid With each other itis thus possible by a proper combination of the rate of electrolysiscarried out under use of 1:1 compound and NaAl(C H in the anolyte andthe corresponding continuous replenishment of the catholyte containingthese compounds to arrive at such a point that the condition in theanode space required in accordance with the invention, i.e. the presenceof the 1:1 compound and sodium aluminum tetraethyl in the anolyte willbe invariably maintained during an electrolytical process of any givenlength of time. In this manner, the critical limit is never exceededbeyond which free aluminum triethyl is formed in the anolyte.

In accordance with a preferred embodiment of the process of theinvention part of the catholyte is thus continuously withdrawn from theelectrolysis device, mixed with aluminum triethyl in an amountapproximately equivalent to the amount of aluminum separated from theremoved part of the catholyte and the combined liquid added to the anodespace from which a corresponding amount of anolyte is continuouslywithdrawn, freed of the lead tetraethyl and subsequently introduced intothe cathode space.

This removal can be carried out at any given electrolye compositionduring the electrolysis provided the catholyte already contains the 1:1compound and so dium aluminum tetraethyl. The higher the concentrationof 1:1 compound and sodium aluminum tetraethyl in the catholyte is, thesmaller may be the volumes to be removed. For economic reasons it issuitable to keep the Withdrawal rates of the liquids to be exchanged aslow as possible. The separation of lead tetraethyl outsidde theelectrolysis device can thus, for example, be effected more easily fromsmaller amounts of anolyte than if the amounts of anolyte to be Workedup are large and obtained at high removal rates. Moreover, if theconcentration of 1:1 compound and sodium aluminum tetraethyl in thecatholyte is high, a higher yield of lead tetraethyl per volume anolytecan be obtained than if these compounds are present in smallerconcentrations in the catholyte part to be introduced into the anodespace.

In the case of a continuous exchange of the electrolytes theelectrolysis is thus suitably started with the same electrolytecomposition than when working intermittently. The electrolysis is nowcontinued until the sodium aluminum tetraethyl, preferably however the1:1 compound has approximately disappeared under formation of the 1:2compound in the anolyte, without exceeding this limit. From this pointon small proportions of catholyte are continuously withdrawn from thecathode space, mixed with an amount of aluminum trialkyl approximatelyequivalent to the amount of aluminum separated from the thus removedliquid amount and passed into the anode space from which a correspondingamount of anolyte is continuously withdrawn, freed of the leadtetraethyl and subsequently introduced into the cathode space. Thecontinuous process, as compared with the intermittent process is thuscharacterized by the fact that while both processes start with the samecomposition of catholyte and anolyte, a stationary state is obtained inthe continuous process in which the electrolyte composition in thecathode and anode space are approximately the reverse of the compositionat the beginning of the electrolysis. Contrary thereto, no suchstationary composition of the electrolyte is obtained in an intermittentexchange process, where the composition of the speassa electrolytevaries intermittently between the two limits at the beginning and theend of one charge.

Already in the said prior application Serial No. 548,862, it was pointedout that the aluminum trialkyl used for the production of theelectrolyte and also the aluminum trialkyl which is constantly addedmust be free from any hydride. This requirement applies also to theprocess of this invention. It for example even a small amount of A1R2His contained in the electrolyte, the latter becomes immediately dark incolour as a result of the reaction with the formed lead tetraalkyl andthe formation of lead. The removal of any hydride present may beeffected in the manner described in application Serial No. 548,862 bytreating the aluminum trialk-yl or the electrolyte with olefins attemperatures between 60 C and 70 C.

For reasons of economy it is desirable to carry out the electrolysis atthe highest possible temperatures since the conductivity of theelectrolyte baths used increases greatly with increasing temperatures.On the other hand, the upper range of the electrolysis temperatures to.be used is limited by the fact that in the case of excessively hightemperatures, in particular during a prolonged electrolysis, theelectrolyte will again become dark colored. For the process of theinvention, temperatures between the solidification point of theelectrolyte mixture (in most cases in the range of room temperature andabout 40 C.) and about 110 C. are suitable, temperatures between 60 C.and 80 C. are preferred. A temperature of the electrolyte of about 70 C.is particularly suitable. This temperature permits the safe working forany length of time without the appearance of any interfering sidereactions in the electrolyte composition. For short periods of time,somewhat higher temperatures may also be applied.

According to the invention, the liquids used in the anode and cathodespace are cooled during the electrolysis in order to obtain atemperature of about 70 C. This measure is necessary since the specificheat of the electrolyte is relatively low so that the amount of energyadded during the electrolysis would excessively increase the electrolytetemperature within a short time. According to the invention this coolingis effected with particular advantage by working not with stationary butwith flowing electrolytes.

Substantially larger volumes of anolyte and catholyte liquids than arerequired to fill the electrode spaces may be separately cycled throughthese spaces and cooled outside the electrolysis device. In this manner,it is possible to regulate the exit temperature of the electrolyteliquid by an appropriate selection of flow rate and entering temperatureof the electrolyte into the electrolysis device. In accordance with theinvention, the temperature diflference of the electrolyte at theentrance and exit point amounts preferably to 5 C. in particular to 2-4C. When working in this manner, there are obtained a number of furtheradvantages in addition to the easy and reliable adjustment of thetemperature of the electrolyte. For example it is not necessary toprovide a complicated cooling system in the electrolysis cell whichpermits the construction of the cell in a very compact and economicalform.

Furthermore there are obtained other considerable advantages for theunimpeded execution of the process of the invention. it has already beenpointed out that as a result of the higher current densities which aredesirable for economic reasons, the aluminum is deposited at the cathodeas a loose finely divided crystalline powder. According to theinvention, this metal powder can easily be scraped from the cathode andsubsequently discharged from the electrolysis device together with theflowing catholyte. The operation in the anode space is also considerablysimplified as a result of the cyclical anolyte flow according to theinvention. The 2:1 electrolyte possesses a certain solubility for theformed lead tetra- When working with an electrolyte temperature of 70 C.in the cell, the anolyte would for example only then separate liquidlead tetraethyl as second phase, it the content of the latter would beabove 11%. As a result of the cyclically flowing anolyte according tothe invention it is now easily possible to cool the anolyte outside theelectrolysis cell to temperatures wihch are sufiiciently low so as notto exceed a predetermined maximum lead tetraethyl content in the anolyteliquid. The lower limit of this low temperature is restricted by thesolidification point of the anolyte which is higher at the beginning ofoperation when there is still a great amount of 1:1 compound and NaAl (CH present than towards the end when the composition approaches the 1:2compound. On the other hand the solubility of the lead tetraethyl in theelectrolyte is somewhat smaller at the beginning than at the end. Incase of an intermittent execution of the process, it is of courseequally possible to maintain the temperature of the total supply ofanolyte at about 70 C. without any separation of lead tetraethyl duringthe entire electrolysis. In this case the total lead tetraethyl formedat the end of the process is still present in dissolved form. It is thenpossible to cool the anolyte to such a degree, for example 5 C. that thelarger proportion of the formed lead tetraethyl is separated out atonce. With an anolyte which contains at the end of the operationapproximately 10% lead tetraethyl itis thus possible to separate about7080% lead tetraethyl in pure form.

Subsequent to the separation of the main lead tetraethyl content theelectrolytically exhausted anolyte must in any case be completely freedof any lead before it can be used as catholyte.

According to the invention, a particularly suited process for thisseparation is the liquid-liquid counter current extraction. Theextraction may be carried out in particular with hydrocarbons, ifdesired under pressure. An excellent extracting agent is for exampleisooctane. The distribution coetficient, for instance, of leadtetraethyl in isooctane and 1:2 compound amounts to 16:1. In anextraction with three theoretical steps it is thus very easy to arriveat a very small lead content of for example 1 mg./ cm. The volume ofisooctane required for this extraction corresponds approximately to thatof the electrolyte, the isooctane dissolving some of the electrolyte.Upon stripping off the isooctane, the residue separates, however, intotwo layers; one consisting of a small amount of electrolyte which isreturned to the extraction, the other of lead tetraethyl. This type ofextraction, however, presents the difficulty that as result of the leadtetraethyl content the density of the extraction agent approximates thedensity of the electrolyte to such a degree, that during the extractionwith the first portion of extracting agent the layers separate onlyslowly, whereas this difliculty is not encountered with the subsequentportions used in the extraction.

Thus, according to the invention an extraction agent is suitably addedto the electrolyte in the beginning. This indifferent agent may bepresent in amounts of from 3 to 10% vol. of the electrolyte, theelectrolyte being preferably saturated therewith. The electrolyteabsorbs for example 5 cm. isooctane per 100 cm. electrolyte. By acarefully measured addition of a minute amount of additional extractionagent subsequent to the electrolysis and by cooling to, for example 0 C.it is possible to more easily extract larger amounts of lead tetraethyl.imultaneously the volume of the lead tetraethyl to be separated is thusincreased. This constitutes an additional advantage of the processaccording to the invention since experience has shown that theextraction of a small amount of a second layer from a large amount of afirst layer presents certain difficulties. Since only negligible amountsof extraction agents are used up during the first step of the improvedextraction of lead tetraethyl from the anolyte, it is thus possible tocarry out a same number of further extractions, for instance, five withthe same total amount of extraction agent.

When proceeding in this manner, and using for example isooctane asextraction agent for the separation of lead tetraethyl, the finalconcentration of lead tetraethyl in the electrolyte amounts to aboutonly one-fifth of the amount obtained if the extraction agent is notadmixed with the electrolyte in the beginning.

The remaining traces of lead in the anolyte can be removed by anafter-treatment of the anolyte, for instance with a small amount offinely divided aluminum, the finely divided aluminum obtained from theprocess itself being particularly suitable since it shows a highactivity for this reaction.

As has already been pointed out, the carrying out of the processaccording to the invention requires a reliable separation of catholytefrom anolyte without, however, substantially interfering with thecurrent transport. According to the invention, this is accomplished byseparating the cathode from the anode space by the use of at least onediaphragm. In principle any material may be used for this purpose whichunder the operating conditions prevailing in the electrolysis devicewill preserve its stability against the relatively corrosive electrolyteover a longer period of time and the selective effect of which suflicesto retain the larger ions and the aluminum and lead ethyl compounds andcomplexes in their respective electrode spaces without any substantialinterference with the current transport by the smaller sodium andfluorine ions.

It has been surprisingly found that cellulosic products are a suitablematerial for these diaphragms, and are resistant against the chemicaleffect of these electrolytes even at temperatures of about 100 C. Alltypes of porous cellulosic products with sufficiently small pores maythus be used. It is preferred to use filter paper as diaphragm material.Suitable are for example materials of which a round filter with a crosssection of cm. shows a filter rate for 100 cm. distilled water at C. anda height of the column of water of 6 cm. in the range of to 200 see. Aparticularly suitable material is filter paper which has been compactedor chemically impregnated in order to reduce the size of the pores. Inthis manner, it is possible to use diaphragms with a thickness of only afew tenths of a mm. In order to increase the mechanical resistance,these diaphragms may be reinforced by a filter consisting of cloth or byinserting the diaphragm between a fabric such as cotton. Other suitablediaphragm materials are for instance glass fiber webs or fabrics.

Any slow transfer of the anolyte into the cathode chamber through thediaphragm which may possibly still occur can easily be eliminated bymaintaining a definite difference in the electrolyte levels. Thisdifference in level is adjusted in such a manner that during the entireprocess a slow flow from the cathode into the anode space through thediaphragm is maintained or that this difference in level prevents atleast a transfer of the anolyte into the cathode space. The diflferencein level to be maintained depends upon the pore size of the diaphragm sothat with a diaphragm with very fine pores a lower difference in levelcan be chosen than in the case of a diaphragm with coarse pores.Inasmuch as the total electrical resistance of the cell on the otherhand is largely dependent upon the pore size of the diaphragm, the besttechnical effect consists in a compromise between these opposinginfluences which can very easily be established by a few experiments.

Alternatively, the reliable separation of anode and cathode space may beobtained by an auxiliary measure in accordance with the invention. Withthe help of at least one additional diaphragm, a center space for thereception of an electrolyte can be formed between the anode and cathodespaces. An electrolyte, which preferably does not contain any lead, canbe conducted through the center space in a slow stream. It absorbs thelead tetraethyl portions transferring over from the anode space andcarries them immediately out of the electrolysis device. In this manner,the catholyte can also be reliably protected against the diffusion ofany lead compounds. After leaving the electrolytic cell, the electrolyteflowing through the center space may, if necessary, be purified from anylead by addition of traces of finely divided aluminum, suitably from theprocess itself, and subsequently recycled.

The operation of the anode space during the electrolysis is relativelysimple. It is merely necessary to replace the used up proportions oflead by fresh lead. This may, for instance, be readily accomplished byfeeding lead rods through an opening provided for this pur pose into theanode space in the same amount in which they are being used up duringthe electrolysis.

At the cathode, aluminum is deposited during the electrolysis. Withoutany special precautionary measures, this aluminum would be deposited atthe cathode in the form of crystals and might conceivably thus increasethe volume of the cathode until it reaches the diaphragm which it mayeven pierce. It is therefore necessary to prevent this accumulation oflarge amounts of aluminum crystals at the cathode. Good results areobtained, for example, by the provision of mechanical stripping meanssuch as rods, grids, frames, etc. with cathode and stripping means aremoved relatively to each other. Thus, it is possible to maintain thecathode stationary and to move the stripping means or to fix thestripping means and to move the cathode. However, it is equally possibleto effect the removal of the aluminum from the cathode by means ofhydraulically working stripping means. At the required higher currentdensities the aluminum is deposited at the cathode in-finely dividedform and by selecting an appropriate flow rate of the catholyte, thefinely divided aluminum can be separated from the cathode and removedfrom the electrolysis device by the flowing electrolyte. This hydrauliceffect may, if necessary, be enhanced by adding mechanically actingstripping elements, such as small balls of glass or metal to theelectrolyte which are then carried along in the circulating stream.During this circulation, these balls strike the loose aluminum powder atthe cathode and remove it. These mechanically working stripping elementsare separated from the aluminum particles contained in the electrolyteoutside the electrolysis device.

Occasional troubles connected with the removal of the aluminum from thecathode which might still occur, can be corrected by cleaning thecathode completely by means of a temporary reversal of the direction ofthe current and without necessitating any complicated mechanicalmeasures, such as the dismantling of the electrolysis device.

In order to facilitate the removal of the aluminum from the cathode, thecathode is suitably so developed that larger amounts of aluminum canonly be deposited at the cathode with difficulty. Thus, continuous metalplates are suitably not used as cathode, but the cathode is preferablyconstructed in such a manner that it consists of individual metalsegments inserted in a carrier plate. According to the invention, thecathode may, for example, consist of metal wires embedded in a frameplate, preferably in oblique direction. The use of these metal wiresprovides for a particularly high current density in the conductive partsof the cathode thereby increasing the deposition of aluminum in finelydivided form. Moreover, the aluminum can accumulate only at these metalwires. If, for instance, mechanical scrapers are used, this finelydivided aluminum can be spread over the whole carrier plate. But byappropriate choice of the material of which the carrier plate consiststhe adherence between aluminum and carrier plate can be so minimizedthat the aluminum is easily removed therefrom.

Any materials may be used for the construction of cathode plate and theelectrolysis device as a whole, which are not electrically conductiveand which permit the safe carrying out of the electrolysis with thehighly reactive and self-inflammatory electrolytes without giving anychemical change in the materials themselves or in the electrolytes.Particularly suitable materials for the electrolytic cells and thecarrier plate of the cathode are laminated press materials of syntheticresins, especially Bakelite (phenol formaldehyde) resins, which may bestrengthened with fabrics in order to increase their elasticity. Thismaterial permits the easy construction of the individual parts of thecells which have to be very carefully executed. Another suitablematerial is for example wood impregnated with polyethylene or with highmelting paraflines. According to the invention, annealing lacquers of anepoxy resin have proven themselves as particularly suitable protectionfor those metal parts not designed for current transfer to theelectrolyte.

As has already been pointed out, the conductivity of the electrolyteaccording to the invention increases with increasing temperatures.However, in the process of the invention the conductivity of theelectrolyte mixture is restricted by the mentioned limitation of thereaction temperatures to about 70 C. At the reaction temperatures to beused in accordance with the invention, the resistance of the electrolyteis still comparatively high. Inasmuch as the voltage in the electrolysiscell should not exceed 2-10 volts, and preferably not volts for reasonsof limiting the consumption of electrical energy and furthermore sincefor various reasons higher current densities of about 315 amperes/dmF,preferably 5-10 amperes/dm. are preferred (separation of aluminum inform of finely divided powder, restriction of size of cells, etc.) it isclear that one must Work with electrodes which are spaced relativelyclosely together. Otherwise, it is either necessary to increase thevoltage excessively or to reduce the current density too much. Accordingto the invention, a distance between the electrodes of about 1 cm. isparticularly suitable. At the reaction temperatures to be used one canthen work with a voltage of about 5 volts and a current density of about5 amperes/dm. It is equally possible to select smaller distances betweenthe electrodes for the electrolysis. In the technical application of theprocess according to the invention the combination of the largestpossible number of individual electrolytic cells in such a manner thatthey can be simultaneously operated in a simple way is recommended.Practically all devices which permit the simultaneous operation of anydesired number of electrolysis cells are thus suitable. spaces areconnected with each other and anode spaces are connected with each otherin such a manner, that electrolyte liquid from all of the cathode spacesis passed to and recycled back from a common supply and in the samemanner electrolyte liquid from all of the anode spaces is passed to andrecycled from a common supply. The cooling and if necessary treatment ofthe electrolyte can be effected at these common supplies. In a fully continuous process in which a certain proportion of anolyte and catholyteis continuously withdrawn and passed after appropriate preliminarytreatment to the other electrode space, the electrolyte proportions tobe exchanged are suitably each taken from a different one of the commonsupplies, the anolyte freed of tetraethyl lead; the catholyte mixed withthe necessary amount of aluminum triethyl and each, subsequentlyintroduced into the other common supply.

In this combination of individual electrolysis cells into one largeelectrolysis device the parts which require Preferably the cathode 1.2mechanical movement are suitably moved together for example by a leversystem.

An electrolysis device suitable for the technical execution of theprocess is diagrammatically shown in FIG. 1. This device has the anode 1and cathode 2 in the form of frame shaped plates which are stacked inalignment side-by-side, separated by the diaphragms 3 and 4. A wholeseries of alternately positioned anode and cathode plates 1 and 2, eachseparated by a diaphragm, such as diaphragms 3 and 4, may thus bepositioned together allowing a combination of individual electrolysiscells. The plates may be pressed together in position in any desiredmanner as, for example, in the manner of a filter press, and at each endthere may be positioned an end plate such as the end plate 5 made ofinsulating material as, for example, synthetic resin orthe like. Thehollow spaces in the interior of the frames serve to hold theelectrolyte liquid and suitable openings or conduits may be providedthrough the tops and bottoms of the frames for the introduction andwithdrawal of the electrolyte. The anode plate is, of course, alead-containing plate, and the cathode plate may be formed, for example,of an insulating material, such as synthetic resin, or the like havingbodies such as wires, or the like, of the conducting metal of thecathode, such as iron, aluminum, copper, brass, or the like, embeddedtherein. It is also possible to press suitable gaskets or packings ofelectric insulating material between the individual frame plates, suchgaskets serving to prevent leakage of the electrolyte, and to insulatethe plates one from another.

As has already been mentioned, the carrying out of the process accordingto the invention is however not limited to an electrolysis device ofthis type. Any device may be used which prevents the comingling ofanolyte and catholyte.

Inasmuch as the electrolyte used in accordance with the invention isextremely oxygen-sensitive and self-igniting it is preferably to carryout all operations in an inert gas.

The invention will be described in further detail in the followingexamples which are given by way of illustration and not limitation. Inthese examples the following compounds are used for the electrolytes:

(a) Sodium aluminum triethyl fluoride (NaAl(C H F) (b) Sodium fluoridealuminum triethyl (1:2 compound) (NaF.2Al(C H (0) Sodium aluminumtetraethyl (NaAl(C H These three compounds are self-igniting and musttherefore be handled in an inert atmosphere. The compounds (at) and (b)are obtained by mixing sodium fluoride and 1 mole or 2 moles aluminumtriethyl at C. for one hour with stirring. Compound (0) is obtained bymixing aluminum triethyl at C. with metallic sodium in a molar ratio of4:3 with stirring followed by separation of the deposited aluminum fromthe melt (cf. A. von Grosse and J. M. Mavity, Journal of OrganicChemistry 5, 1940, page 111).

The electrolysis device used in the examples consists in the simplestcase as shown in FIG. 2 merely of a lead plate 5 as anode and an equallylarge plate 6 consisting of a different metal,-such as iron, aluminum,copper or brass as cathode. Anode and cathode are disposed parallel toeach other and spaced 1 to 2 cm. apart. The plates are surrounded by anelectrically insulating material corresponding to the plates in shapeand form forming for example the container 8. In the middle between thetwo plates and parallel to them there is a thin diaphragm 7, dividingthe container into spaces 9 and M. It is suitably formed of filter paperwhich is protected on both sides by a fabric consisting of cellulose orglass fibers. In the space M between diaphragm and cathode there isarranged a frame 11 which is covered with electrically insulatingstripping wires 12, this frame being moved to and fro when in operation.Anode and cathode spaces have openings through which liquid electrolytesmay be introduced from the top and discharged at the bottom. In the caseof larger runs several individual cells are suit ably combined as shownin FIG. 1. In that case, anodes and cathodes are utilized on both sides(apart from the first and the last element). The frames may be providedwith apertures at the top through which it is possible to move thestripping means in the cathode spaces and to replace the lead plates inthe anode spaces. It the lead plates have a thickness of 0.5 to 1 mm. itis easily possible to replenish the lead continuously. It was found tobe suitable to use in place of cathodes consisting of massive metalplates equally large cathodes consisting of electrically insulatingmaterial in which obliquely disposed metal wires are embedded.

All runs described in Examples 1 to 4 are carried out in an inertatmosphere of nitrogen or argon.

Example 1 The catholyte consists of the compound NaF.2Al C H 3 Theanolyte is obtained by mixing 14.85 kg. NaAl(C H (c) 13.87 kg. NaA1(C HF (a) and 40.78 kg. NaF.2Al(C H (b) Anolyte (69.5 kg.) and catholyte(64.8 kg.) are filled into two storage chambers (13 and 14) above thecontainer 8 and heated to 70 C. The anode 5 has a free surface of 25 dm.Anolyte and catholyte are allowed to flow through the anode space andthe cathode space respectively of the electrolysis device. The flow rateamounts to approximately 4 liters per minute. The aluminum formed at thecathode 6 is scraped by the mechanically moved stripping means 11 andcarried out of the device in the liquid stream. The electrolysis iscarried out with an amperage of 200 amperes, or a current density of 8amperes/dmF. The terminal voltage amounts to 8 volts. The resulting heatdue to the current causes an increase in temperature of 3 to 4 C. in theelectrolyte efiluent, as compared to the entering electrolyte. Theanolyte fiows through the line 15 into a storage vessel 16 from .whereit is pumped by the pump 17 through line 18 into the upper storagechamber 13. Upon leaving the electrolysis device the catholyte is firstled through line 19 into a cylindrical separating chamber or settlingtower 20 where the electrolytically separated aluminum which is carriedalong in the flowing catholyte is separated. The catholyte freed of thealuminum flows through line 21 into a storage chamber 22 from which itis recycled through line 23 into the upper storage chamber 14 by meansof pump 24. The heat loss in the entire device is so considerable that aspecial cooling of the electrolyte is in general not required. However,if necessary, it may be effected in the upper storage chambers 13 and14.

At a current passage of 200 amperes, the anolyte is exhausted after 12hours of electrolysis. The 72.0 kg. anolyte are mixed with 10 liters dryisooctane and cooled to C. Hereby, the anolyte separates into twophases. The lower layer of 9.65 kg. consists of 5.1 kg. lead tetraethyland 4.55 kg. isooctane. The upper layer is composed as follows:

64.8 kg. NaF.2Al(C H 1.8 kg. Pb(C:, H and 2.5 kg. isooctane Uponaddition of isooctane and cooling to 0 C. it is thus possible toseparate 75% of the formed lead tetraethyl from the anolyte. Theelectrolyte which still contains lead is now extracted with 32.4 litersisooctane in a 3-step extraction centrifuge in a countercurrent. Uponcompletion of the extraction, the electrolyte still contains about 3 g.Pb(C H /65 liters. it is thus practically 14 free of any lead compound.The electrolyte now has the composition NaF.2Al(C H and may be safelyused as catholyte for a new electrolysis.

The extract containing 1.8 kg. lead tetraethyl is combined with thelower phase obtained by the cooling of the anolyte. Its content oforgano-aluminum compounds is low and amounts to about 600 g. NaF.2Al(CI-I The isooctane used as extraction agent is distilled off in vacuo ata pressure of 70 mm. Hg at 50 C. and can be used for furtherextractions. The lead tetraethyl is subsequently distilled oil in vacuoat 45 C. and 0.5 mm. Hg; the distillation residue of about 600 g.NaF.2Al(C H is recycled into the next extraction.

At the end of the electrolysis the catholyte has the followingcomposition:

14.84 kg. NaAl(C H 18.50 kg. NaAl(C- H F amounting to a total of 66.15kg. This mixture is stirred with 3.4 kg. aluminum triethyl; the thusobtained reaction product consists of 14.85 kg.NaAl(C H 2400 amperes/hr.

Example 2 The process of Example 1 is repeated, the catholyte beingagain NaF.2Al(C H The anolyte, however, has the following composition:

29.7 kg. NaAl(C H 27.7 2 5)s 12.1 kg. NaF.2Al(C H At a current passageof amperes and a terminal voltage of 6 volts the anolyte is exhaustedafter 48 hours. The isolation of the lead tetraethyl is effected in thesame Way as in Example 1. The lead tetraethyl yield amounts to 14.1 kg.or 98% of the amount calculated for 4800 ampere hr.

Upon completion of the run any liquid electrolyte still present in theseparation vessel 20 is siphoned oif from the deposited finely dividedaluminum. The aluminum is suspended in 13.5 kg. aluminum triethyl andtransferred into a rotating autoclave with a capacity of 50 liters.

A pressure of about 250 atmospheres electrolytic hydrogen is applied andthe autoclave heated to C. and rotated. After about 2 to 3 hours thepressure has decreased by 200 atmospheres and remains constant afterthat. The reaction is finished. After cooling, excess hydrogen is blownoff. Subsequently a pressure of 20 to 30 atmospheres ethylene is appliedand the autoclave again heated with rotation to 60 to 65 C. Theapplication of ethylene pressure is repeated several times. After threehours the addition of ethylene is finished. After blowing oil the excessethylene a small sample of aluminum triethyl is taken from the autoclaveand mixed with a few drops of lead tetraethyl. If this sample does notbecome dark in color as a result of the precipitation of lead, then thealuminum triethyl obtained does not contain any diethyl aluminum hydrideand can be used for the regeneration of the electrolyte. If the samplestill becomes dark colored the treatment with ethylene has to berepeated. There are obtained 20.23 kg. aluminum triethyl, i.e. 6.73 kg.or 100% of the theoretical value have been formed.

15 The 6.73 kg. aluminum triethyl are admixed to the catholyte which hasthen the following composition:

29.7 kg. NaAl(C H )4 12.1 kg. NaF.2Al(C I-I it is then ready to be usedas anolyte during the next electrolysis.

Example 3 Example 1 is repeated using the arrangement shown in FIG. 3.fter passage of 2400 ampere hr., i.e. of 200 amperes during anelectrolysis of 12 hours a liquid stream is branched otf from thecathode cycle at 25 at a rate of 5.5 kg./ hr. To this a stream ofaluminum triethyl is admixed from container 26 at a rate of 284 g./hr.The mixture is allowed to flow through line 27 into the upper storagetank 13. Simultaneously a liquid stream of 6.0 kg./ hr. is removed fromthe anode cycle at 28 and cooled to C. in cooler 29. The lower phaseformed is separated and subjected to a continuous counter-currentextraction in the extraction centrifuge St The electrolyte now free ofany lead is led through line 31 to the upper storage chamber 14 for thecatholyte. Under these circumstances the electrolysis may be continuedas long as desired.

Example 4 If the electrolytically deposited aluminum is not to be usedfor the production of aluminum triethyl but is to be recovered asrefined aluminum, the following modification of the process is possible:

The process is carried out as described in Examples 1 to 3. Uponextraction of the anolyte with isooctane the electrolyte still containsabout 40 mg. lead tetraethyl per liter. If this electrolyte is now usedas catholyte the separated aluminum will always contain traces of lead.In order to free the electrolyte of the small amounts of lead compound,the anolyte is intensely stirred about half an hour at 70 C. after theextraction with about 80 g. of the electrolytic aluminum. Subsequentlythe aluminum is allowed to settle. The electrolyte is siphoned off. Nolead earl be found in the electrolyte by chemical-analyticaldetermination; this may then be used in the subsequent electrolysis ascatholyte. The aluminum used for the precipitation of the last traces oflead can be repeatedly used for the same process. This operating step issuitable also if the aluminum is to be converted again to aluminumtriethyl since an aluminum completely free of any lead reacts morequickly with aluminum triethyl and hydrogen.

We claim:

1. In the process for the electrolytic production of tetraethyl lead bypassing an electrolysis current between a cathode and lead containinganode through an alumi num triethyl containing electrolyte, theimprovement which comprises maintaining a diaphragm between the cathodeand anode to thereby form separate cathode and anode spaces and at leastinitially maintaining as the electrolyte in said anode space an anolyteessentially consisting of NaAl(C H and NaF.Al(C H said NaAl(C H andNaF.1 il(C H being present in substantially equivalent amounts, saiddiaphragm substantially preventing migration of electrolyte between thecathode and anode spaces without substantially interfering with thepassage of said current.

2. Improvement according to claim 1 in which said anolyte additionallycontains NaF.2Al(C H 3. Improvement according to claim 2 in which NaAl(CH and NaF.Al(C H are present in substantially equivalent amounts and inwhich about 0.16 to 1.70 moles of NaF. 2Al(C H are present per mole ofNaF.Al(C H 4. Improvement according to claim 3 in which not more thanabout 33 /366 /s ampere-hours/kg. electrolyte are used for theelectrolysis.

5. Improvement according to claim 4 in which about 0.671.70 moles ofNaF.2Al(C I-I are present per mole of NaF.Al(C H and in which theelectrolysis is effected with about 50 ampere-hours/kg. electrolyte.

6. Improvement according to claim 1 in which the electrolysis iscontinued until one of said NaAl(C H and NaF.Al(C H has beensubstantially completely exhausted.

7. Improvement according to claim 1 which includes substantiallycontinuously removing anolyte from said anode space and substantiallycontinuously replacing the removed anolyte with fresh anolyte.

8. Improvement according to claim 1 which includes maintaining as theelectrolyte in said cathode space a catholyte comprising NaF.2Al(C H I vV 9. Improvement according to claim 1 which includes at least initiallymaintaining as the electrolyte in said cathode space a catholyteessentially consisting of a mixtlll'fi 'Of and NaF.Al(C H 10.Improvement according to claim 1 in which an aluminum triethylcontaining electrolyte is maintained in said cathode space as catholyteand which includes after at least partial exhaustion thereofregenerating the catholyte by the addition of an amount of aluminumtriethyl substantially equivalent to the amount of aluminum deposited atthe cathode.

11. Improvement according to claim 1 which includes removing exhaustedanolyte from said anode space, freeing the same of tetraethyl lead andrecycling the same to said cathode space .as catholyte.

12. Improvement according to claim 1 which includes substantiallycontinuously removing anolyte from said anode space passing the same toa body of excess anolyte and recycling anolyte from said body back tostaid anode space and which includes substantially continuously removingcatholyte from said cathode space passing the same to a body of excesscatholyte and substantially continuously recycling catholyte from saidbody back to said cathode space.

13. Improvement according to claim 1 in which the catholyte maintainedin the cathode space is a sodium aluminum tetraethyl-sodium fluoridealuminum triethyl containing catholyte and which includes substantiallycontinuously removing catholyte from the cathode space, and mixing anamount of aluminum triethyl therewith substantially equivalent to theamount of aluminum separated therefrom during the electrolysis andthereafter passing the removed catholyte with the added aluminumtriethyl to the anode space and which includes substantiallycontinuously removing a corresponding amount of anolyte from said anodespace freeing the same of tetraethyl lead and passing the same into thecathode space.

14. Improvement according to claim 1 which includes removing formedtetraethyl lead from the anolyte by cooing to a temperature of at leastabout 0 C.

15. Improvement according to claim 1 which includes removing tetraethyllead formed during the electrolysis from the anolyte by cooling to atemperature of at least 0 C. followed by extraction with an extractionagent.

16. Improvement according to claim 15 in which said extraction agent isisooctane.

17. Improvement according to claim 16 which includes maintaining anamount of isooctane up to the saturation quantity thereof in the anolyteduring said electrolysis.

18. Improvement according to claim 1 in which the electrolyte maintainedin the cathode space is an aluminum triethyl containing catholyte, andwhich includes stripping deposited aluminum from the cathode andsubstantially continuously removing catholyte from the cathode spacecarrying therewith entrained, the stripped aluminum.

19. Improvement according to claim 1 in which said l c y is is e fectedunder an inert gasatmosphere.

20. Improvement according to claim 1 in which said References Cited inthe file of this patent electrolysis is effected with a current densityof between UNITED STATES PATENTS about 3 to 15 amp./dm.

21. Improvement according to claim 1 in which s i 733 315 Hgopes Apr 251905 anode and cathode are frame-shaped plates pos tioned 5 2 3 3 3 7Blcck N0 21 194 side by side in alignment with said diaphragm sand 2 7374 Bodamm- Man 6, 5 Wiched therebetween- 2,844,615 Ziegler et al. July22, 1958 22. Improvement according t0 claim 21, 111 which 2 49 349Ziegler et aL Aug. 2 19 said frame plates are at least partially formedof fiber 2 3 3 394 smith Dec. 9 195g reinforced synthetic resin.

1. IN THE PROCESS FOR THE ELECTROLYTIC PRODUCTION OF TETRAETHYL LEAD BYPASSING AN ELECTROLYSIS CURRENT BETWEEN A CATHODE AND LEAD CONTAININGANODE THROUGH AN ALUMINUM TRIETHYL CONTAINING ELECTROLYTE, THEIMPROVEMENT WHICH COMPRISES MAINTAINING A DIAPHRAGM BETWEEN THE CATHODEAND ANODE TO THEREBY FORM SEPARATE CATHODE AND ANODE SPACES AN AT LEASTINITIALLY MAINTAINING AS THE ELECTROLYTE IN SAID ANODE SPACE AN ANOLYTEESSENTIALLY CONSISTING OF NAAI(C2H5)4 AND NAF.AI(C2H5)3, SAIDNAAI(C2H5)4 AND NAF.A1(C2H5)3 BEING PRESENT IN SUBSTANTIALLY EQUIVALENTAMOUNTS, SAID DIAPHRAMG SUBSTANTIALLY PREVENTING MIGRATION OFELECTROLYTE BETWEEN THE CATHODE AND ANODE SPACE WITHOUT SUBSTANTIALLYINTERFERING WITH THE PASSAGE OF SAID CURRENT.